Organopolysiloxane compositions which can be crosslinked by means of a condensation reaction

ABSTRACT

Moisture curable elastomer compositions are highly suitable for use as sealants, and initially contain an organopolysiloxane having condensable groups, a tri-acyloxy functional organosilicon compound, and as fillers, anhydrite and silica. The compositions have very low modulus and accommodate high joint movement, while being storage stable

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase of PCT Appln. No.PCT/EP2016/050871 filed Jan. 18, 2016, which claims priority to GermanApplication No. 10 2015 201 423.1 filed Jan. 28, 2015, the disclosuresof which are incorporated in their entirety by reference herein.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to organopolysiloxane compositions crosslinkableby condensation reaction, more particularly to one-component,filler-containing organopolysiloxane compositions which crosslink underthe influence of moisture and which crosslink to elastomers withelimination of carboxylic acids such as acetic acid.

2. Description of the Related Art

One-component silicone rubber mixtures which undergo vulcanization toelastomers at room temperature (RTV1 compositions) on ingress of water,and which are storable in the absence of water, are known. Theseproducts are used in large quantities, for example, as joint-sealingcompositions in the construction industry. The profile of propertiesrequires a multitude of product features for the particular end use thatare necessary, in order that the paste can be processed effectively, forrapid and complete curing, and for its function to be fulfilled durablyin the vulcanized state.

The basis of these RTV1 mixtures are polydiorganosiloxanes, terminatedeither with OH groups or with silyl groups which carry hydrolyzablegroups. Through the chain length of the polymers and through the fillersused it is possible to exert influence over key properties of the RTV1mixtures. In sealing applications where the elastic joint is subject toconsiderable movement, accommodation of movement, in particular, is animportant parameter. For the durable fulfillment of function, it isnecessary that this ability to accommodate movement remains stable—itmust not, for example, go down as a result of severe shrinkage.

Influencing variables for the accommodation of movement are, inparticular, the chain lengths of the polymers and the fillers used.Greater chain length enhances accommodation of movement; reinforcingfillers lower it in conjunction with an increasing modulus. For economicand technical reasons, however, only a limited range of polymer chainlengths are available for the production of RTV1 mixtures. Greater chainlengths lead to very high viscosities of the polymers, and so theapplication-ready products are more difficult to process on account ofthe viscosity, which is high. Compensating for this high viscosity bymeans of plasticizers leads to increased volatility, and therefore to agreater loss of weight, with adverse consequences for the fulfillment offunction, particularly with regard to the requirement of highaccommodation of movement. Consequently, fillers offer one option foradjusting the properties. There are, however, certain restrictions onthe selection of the fillers, especially in the case of preparationswhich crosslink with elimination of carboxylic acids, such as aceticacid.

For example, JP 10-316858 and U.S. Pat. No. 5,938,853 A describe the useof coated chalks in order to prevent the release of CO₂ due to thereaction with the acetic acid eliminated from the acetoxysilanes withthe carbonate. As a result of working in a mixer or kneading apparatus,however, the coating may be damaged, and there is release of CO₂,leading to the inflation of cartridges.

DE 34 39 745 A1 describes, alternatively, the use of silicates whichhave been surface-pretreated beforehand. Silicates are slightlyreinforcing fillers, resulting in increasing modulus and fallingdeclining accommodation of movement.

The use of kaolin as a filler for acetic compositions is described in WO2009/080266 AI. Here again, there is a considerable increase in themodulus of the sealants, leading to increased flank exposure in jointapplications. High accommodation of movement is therefore likewise notrealizable.

Further fillers which are compatible with acetic compositions, such asquartz powders, for example, likewise result in low accommodation ofmovement.

SUMMARY OF THE INVENTION

It is an object of the invention to provide organopolysiloxanecompositions which crosslink to elastomers with elimination ofcarboxylic acids such as acetic acid, with the elastomers exhibitinghigh accommodation of movement, and with the organopolysiloxanecompositions, moreover, exhibiting high storage stability, having goodprocessing qualities, exhibiting low shrinkage, and displaying goodwetting behavior. These and other objects are surprisingly andunexpectedly achieved by the invention by use of anhydrite and silica asfiller, the composition being free of kaolin.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Accommodation of movement is to be understood as the compliance with andclassification of a sealant into a class according to ASTM C 920 Chapter4 that forms the basis for the ASTM C 719 measurement (Test Method forAdhesion and Cohesion of Elastomeric Joint Sealants under CyclicMovement, “Hockman Cycle”).

The subject invention is thus directed to organopolysiloxanecompositions crosslinkable by condensation reaction and producible using

-   (1) organopolysiloxanes containing condensable end groups,-   (2) organosilicon compounds containing at least three acyloxy groups    bonded directly to silicon,-   (3) condensation catalysts,-   (4) anhydrite, and-   (5) silicas, in amounts of at least 1 and not more than 15 parts by    weight, preferably not more than 10 parts by weight, based in each    case on 100 parts by weight of organopolysiloxanes (1),    with the proviso that-   (6) no kaolin is used,-   (7) further fillers are used in amounts of at most 25 parts by    weight, preferably at most 15 parts by weight, more preferably at    most 5 parts by weight, based in each case on 100 parts by weight of    organopolysiloxanes (1), and-   (8) optionally further substances, which are used customarily in    compositions crosslinkable by condensation reaction and which are    different from the constituents (1) to (7).

Organopolysiloxanes (1) which contain condensable end groups arepreferably those of the formula

HO(R₂SiO)_(n)H  (I),

whereR may be identical or different and is a monovalent, optionallysubstituted hydrocarbon radical andn is an integer from 500 to 2000, preferably from 600 to 1700, and mostpreferably from 600 to 1300.

It is possible to use one kind of organopolysiloxane (1) or a mixture ofat least two kinds of organopolysiloxanes (1).

Examples of radicals R are alkyl radicals such as the methyl, ethyl,n-propyl, isopropyl, 1-n-butyl, 2-n-butyl, isobutyl, tert-butyl,n-pentyl, isopentyl, neopentyl, and tert-pentyl radicals, hexyl radicalssuch as the n-hexyl radical, heptyl radicals such as the n-heptylradical, octyl radicals such as the n-octyl radical and isooctylradicals, such as the 2,2,4-trimethylpentyl radical, nonyl radicals suchas the n-nonyl radical, decyl radicals such as the n-decyl radical, anddodecyl radicals such as the n-dodecyl radical; cycloalkyl radicals suchas the cyclopentyl, cyclohexyl, cycloheptyl, and methylcyclohexylradicals; alkenyl radicals such as the vinyl, 5-hexenyl, cyclohexenyl,1-propenyl, allyl, 3-butenyl, and 4-pentenyl radicals; alkynyl radicalssuch as the ethynyl, propargyl, and 1-propynyl radicals; aryl radicalssuch as the phenyl radical; alkaryl radicals, such as o-, m-, andp-tolyl radicals; and aralkyl radicals, such as the benzyl radical andthe α- and the β-phenylethyl radicals.

Examples of substituted radicals R are haloalkyl radicals, such as the3,3,3-trifluoro-n-propyl radical, the 2,2,2,2″,2″,2′-hexafluoroisopropylradical, the heptafluoroisopropyl radical, the chloromethyl radical, andhaloaryl radicals such as the o-, m-, and p-chlorophenyl radicals, andalso all radicals identified above which may be substituted byepoxy-functional groups, carboxyl groups, enamine groups, amino groups,aminoethylamino groups, aryloxy groups, acryloyloxy groups,methacryloyloxy groups, hydroxyl groups, and halogen.

The radical R preferably comprises monovalent hydrocarbyl radicalshaving 1 to 18 carbon atoms, which are optionally substituted by halogenatoms, amino groups, ether groups, ester groups, epoxy groups, mercaptogroups or (poly)glycol radicals, the (poly)glycol radicals beingconstructed more particularly of oxyethylene and/or oxypropylene units.With particular preference the radical R comprises alkyl radicals having1 to 12 carbon atoms, more particularly the methyl radical.

The organopolysiloxanes (1) preferably compriseα,ω-dihydroxydialkylpolysiloxanes, more preferablyα,ω-dihydroxypolydimethylsiloxanes.

Examples of organopolysiloxanes (1) are (HO)M₂SiO[SiM₂O]_(x)SiM₂(OH),(HO)M₂SiO[SiM₂O]_(x)[SiMePhO]_(y)SiM₂(OH),

where Me is methyl radical and Ph is phenyl radical, it being possiblefor the individual units to be distributed randomly in the molecule,where x is a number from 500 to 2000, preferably 600 to 1700, morepreferably 600 to 1300, and y is a number such that y/x is preferably0.01 to 0.1.

The inventively employed organopolysiloxanes (1) preferably have aviscosity of 10,000 to 700,000 mPa·s, more preferably of 20,000 to400,000 mPa·s, and most preferably 50,000 to 200,000 mPa·s, in each caseat 25° C.

The organopolysiloxanes (1) are commercial products and/or may beproduced by methods which are commonplace within silicon chemistry.

As organosilicon compounds (2) containing at least three acyloxy groupsbonded directly to silicon, preference is given to usingacyloxy-functional silanes of the formula

R¹ _(d)Si(OC(═O)R²)_(4-d)  (II)

and/or their partial hydrolysates having up to 10 silicon atoms, whereR¹ may be identical or different and is a monovalent, optionallysubstituted hydrocarbyl radical,R² may be identical or different and is a monovalent, optionallysubstituted hydrocarbyl radical, andd is 1;examples of radicals R are as defined for radicals R¹.

The radical R¹ is preferably a hydrocarbyl radical having 1 to 6 carbonatoms, more preferably a methyl, ethyl, propyl, vinyl or phenyl radical.

Examples of radicals R are as defined for radicals R².

The radical R² is preferably a hydrocarbyl radical having 1 to 6 carbonatoms, more preferably the methyl, ethyl, propyl, vinyl or phenylradical, and most preferably the methyl radical.

Organosilicon compounds (2) containing acyloxy groups are preferablyused in amounts of 5 to 20 parts by weight, more preferably 8 to 15parts by weight, based in each case on 100 parts by weight oforganopolysiloxanes (1).

It is possible to use one kind of organosilicon compound (2) or amixture of at least two kinds of organosilicon compounds (2).

In place of the organopolysiloxanes of the formula (I) it is alsopossible to use those organopolysiloxanes (1′) which are producible byreaction of organopolysiloxanes (1) having condensable end groups withorganosilicon compounds (2) having acyloxy groups, optionally in thepresence of condensation catalysts (3). Preferred in this case are thoseof the formula

(R²(O═)CO)_(3-d)R¹ _(d)SiO(R₂SiO)_(n)SiR¹ _(d)(OC(═O)R²)_(3-d)  (I′),

where R, R¹, R², d, and n have the definition stated for them above.

The organopolysiloxanes (1′) here preferably have a total Si-bondedacyloxy group content of 1200 to 6000 ppm by weight, more preferably of1500 to 5000 ppm by weight, and most preferably 1800 to 4000 ppm byweight, with R² having the aforementioned definition.

The organopolysiloxanes (1) or (1′) used in accordance with theinvention are preferably liquid at room temperature (25° C.) under thepressure of the surrounding atmosphere, i.e., at between 900 and 1100hPa.

Condensation catalysts (3) used may be tin-free condensation catalysts(3a) or tin-containing condensation catalysts (3b).

Examples of tin-free condensation catalysts (3a) are organic compoundsof zinc, zirconium, titanium, bismuth, strontium, iron, and aluminum.Preferred among these condensation catalysts are alkyl titanates,titanium chelates, and carboxylates of bismuth, strontium, and zinc.

Examples of tin-containing condensation catalysts (3b) are organotincompounds such as di-n-butyltin diacetate, di-n-butyltin dilaurate,di-n-octyltin diacetate, di-n-octyltin dilaurate, and reaction productsof alkoxy group-containing silanes or their oligomers with diorganotindiacylates or diorganotin oxides.

Where tin-free condensation catalysts (3a) are used, they are preferablyemployed in amounts of 50 to 5000 wt. ppm, more preferably 100 to 4000wt. ppm, and most preferably 200 to 3000 wt. ppm, in each casecalculated as elemental metal and based in each case on the total weightof organopolysiloxanes (1).

Where tin-containing condensation catalysts (3b) are used, they areemployed in amounts of preferably 10 to 500 wt. ppm, more preferably 20to 250 wt. ppm, in each case calculated as elemental tin metal and basedin each case on the total weight of organopolysiloxanes (1).

Inventively employed anhydrite (4) is preferably used in amounts of 30to 200 parts by weight, more preferably 50 to 150 parts by weight, andmost preferably 70 to 125 parts by weight, based in each case on 100parts by weight of organopolysiloxane (1).

Anhydrite is a calcium sulfate with up to 0.5 moles of water ofhydration, i.e., CaSO₄.z H₂O with 0<z<0.5, in contradistinction, forexample, to gypsum, which is a calcium sulfate having 2 moles of waterof hydration, i.e., CaSO₄.2H₂O. Corresponding anhydrites are availablecommercially in the form of Anhydrite Super (from Caltra, Mijdrecht, theNetherlands) or Krone HEF (Hilfiger Gipswerke, Osterode, Germany).

Inventively employed silicas (5) used are preferably silicas producedpyrogenically.

The inventively employed silicas (5) preferably have a specific BETsurface area of 30 to 500 m²/g, more preferably 100 to 300 m²/g. The BETsurface area is measured by known methods; in one preferred version, thespecific surface area is measured as BET surface area by means ofnitrogen, BET-N₂, at the boiling temperature of liquid nitrogen,preferably in accordance with Deutsche Industrie Norm DIN 66131 and DIN66132.

In the case of the organopolysiloxane compositions of the invention,further fillers (7) may be used. Examples of further fillers (7) arenonreinforcing fillers, i.e., fillers having a BET surface area of up to50 m²/g, such as quartz, diatomaceous earth, calcium silicate, zirconiumsilicate, zeolites, metal oxide powders, such as aluminum, titanium,iron or zinc oxides and/or their mixed oxides, barium sulfate, talc,silicon nitride, silicon carbide, boron nitride, glass powders andplastics powders, such as polyacrylonitrile powders; and reinforcingfillers, i.e., fillers having a BET surface area of more than 50 m²/g,such as carbon blacks, examples being furnace black and acetylene black,and mixed silicon-aluminum oxides of high BET surface area; fillers infiber form, such as asbestos and also plastics fibers. The statedfillers may have been hydrophobized, by treatment, for example, withorganosilanes and/or organosiloxanes, or by etherification of hydroxylgroups to alkoxy groups. If further fillers (7) are used, they arepreferably talc, carbon black or silicates which do not belong to thegroup of the kaolins.

With preference no further fillers (7) are used.

In addition to the constituents (1), (2), (3), (4), (5), and (7), thecompositions of the invention may optionally comprise further substances(8) which are useful in compositions crosslinkable by condensationreaction and which are different from constituents (1) to (7). Preferredexamples of further substances (8) are plasticizers, fungicides,adhesion promoters, rheological additives, and pigments, and mixturesthereof.

Examples of plasticizers are hydrocarbon mixtures having a kinematicviscosity of less than 7 mm²/s at 40° C., and diorganopolysiloxanesendblocked by triorganosiloxy groups, such as dimethylpolysiloxanesendblocked by trimethylsiloxy groups, preferably having a viscosity of10 to 10,000 mPa·s at 25° C. If plasticizers are used, they arepreferably employed in amounts of not more than 35 parts by weight, morepreferably not more than 25 parts by weight, based in each case on 100parts by weight of organopolysiloxanes (1).

Examples of fungicides are tebuconazole, propiconazole, thiabendazole,carbendazim, butylbenzisothiazolinone, dijodomethyl tolyl sulfone,dichlorooctylisothiazolinone, octylisothiazolinone, and zinc pyrithione.

If fungicides are used, they are preferably employed in amounts of notmore than 2000 wt. ppm, based on the total weight of theorganopolysiloxanes (1).

Examples of adhesion promoters are

glycidyloxypropyltrimethoxysilane,glycidyloxypropyltriethoxysilane,glycidyloxypropylmethyldimethoxysilane,glycidyloxypropylmethyldiethoxysilane,dibutoxydiacetoxysilane,methacryloyloxypropyltrimethoxysilane,methacryloyloxypropyltriethoxysilane,methacryloyloxypropylmethyldimethoxysilane,methacryloyloxypropylmethyldiethoxysilane,methacryloyloxypropyltriacetoxysilane, andmethacryloyloxypropylmethyldiacetoxysilane.

If adhesion promoters are used, they are preferably employed in amountsof not more than 2.5 parts by weight, based on 100 parts by weight ofthe organopolysiloxanes (1).

Examples of rheological additives are treated or untreated castor oils,polyethylene oxides or polypropylene oxides or copolymers thereof,optionally with siloxane units.

If rheological additives are used, they are preferably employed inamounts of not more than 1 part by weight, based on 100 parts by weightof the organopolysiloxanes (1).

Examples of pigments are titanium dioxide, carbon black, metal oxides,metal sulfides, organic pigments or mineral pigments such as spinels,for example.

If pigments are used, they are preferably employed in amounts of notmore than 2.5 parts by weight, based on 100 parts by weight of theorganopolysiloxanes (1).

In one preferred variant version, the organopolysiloxane compositions ofthe invention are produced using

(1) organopolysiloxanes(2) acyloxysilanes and/or their partial hydrolysates,(3) organotin compounds as condensation catalyst,(4) anhydrite, and(5) pyrogenic silica.

In another preferred variant version, the organopolysiloxanecompositions of the invention are produced using

(1) organopolysiloxanes,(2) acyloxysilanes and/or their partial hydrolysates,(3) organotin compounds as condensation catalyst,(4) anhydrite,(5) pyrogenic silica, and(8) plasticizer.

In another preferred variant version, the organopolysiloxanecompositions of the invention are produced using

-   (1) organopolysiloxanes,-   (2) acyloxysilanes and/or their partial hydrolysates,-   (3) organotin compounds as condensation catalyst,-   (4) anhydrite,-   (5) pyrogenic silica, and-   (8) plasticizer based on hydrocarbon mixtures and fungicide.

In another preferred variant version, the organopolysiloxanecompositions of the invention are produced using

(1) organopolysiloxanes,(2) acyloxysilanes and/or their partial hydrolysates,(3) strontium carboxylate as condensation catalyst,(4) anhydrite,(5) pyrogenic silica, and(8) plasticizer.

In another preferred variant version, the organopolysiloxanecompositions of the invention are produced using

(1) organopolysiloxanes,(2) acyloxysilanes and/or their partial hydrolysates,(3) zinc carboxylate as condensation catalyst,(4) anhydrite,(5) pyrogenic silica, and(8) plasticizer.

In another preferred variant version, the organopolysiloxanecompositions of the invention are produced using

(1) organopolysiloxanes,(2) acyloxysilanes and/or their partial hydrolysates,(3) titanium chelate as condensation catalyst,(4) anhydrite,(5) pyrogenic silica, and(8) plasticizer.

For producing the compositions of the invention, all of the constituentsof the respective composition can be mixed with one another in anyorder. This mixing preferably takes place at room temperature under thepressure of the surrounding atmosphere, in other words about 900 to 1100hPa, and preferably the ingress of water is avoided in the course ofthis mixing. If desired, however, this mixing may also take place athigher temperatures, such as at a temperature in the range from 25 to80° C.

The normal water content of the air is sufficient for crosslinking thecompositions of the invention. The crosslinking of the compositions ofthe invention preferably takes place at room temperature. Thecrosslinking can, if desired, also be carried out at temperatures higheror lower than room temperature, for example at −5° to 15° C. or at 30°to 50° C. Crosslinking may also be carried out at water concentrationswhich exceed the normal water content of the air.

The crosslinking is preferably carried out preferably under a pressureof 100 to 1100 hPa, more particularly under the pressure of thesurrounding atmosphere.

A further subject of the present invention are moldings produced bycrosslinking the compositions of the invention.

The elastomers of the invention to which the compositions of theinvention crosslink have the advantage that they have high accommodationof movement.

The elastomers of the invention to which the compositions of theinvention crosslink have the further advantage that they have a modulusof elasticity of less than 0.45 N/mm².

Surprisingly, in spite of high filler content on the part of thecompositions of the invention, elastomers are obtained that have highaccommodation of movement and low modulus.

The compositions of the invention have the further advantage that theyexhibit good storage stability and low shrinkage.

The compositions of the invention can be used for all applications forwhich it is possible to use compositions which are storable in theabsence of water and which on ingress of water crosslink at roomtemperature to form elastomers.

The compositions of the invention are suitable as elastic adhesives orsealants, for the sealing of joints, gaps or junctions, for example inthe sanitary sector, window construction, glazing, with buildingmaterials, construction elements, automobiles, rail vehicles, aircraft,boats, household appliances, and machines.

EXAMPLES

In the examples described below, all viscosity figures are based on atemperature of 25° C. Unless otherwise indicated, the examples below areconducted under the pressure of the surrounding atmosphere, i.e.,approximately at 1000 hPa, and at room temperature, i.e. atapproximately 23° C., or at a temperature which comes about when thereactants are combined at room temperature without additional heating orcooling, and also at a relative atmospheric humidity of approximately50%. Furthermore, all data in parts and percentages, unless otherwiseindicated, are by weight.

For the purposes of the present invention, the viscosities aredetermined as follows:

The measurements of the dynamic viscosity of the organopolysiloxanes arebased on DIN 53019-1 on a plate/cone rotational viscometer featuring acone with a diameter of 50 mm and a cone angle of 2°, at 25° C. with ashear rate of 1 1/s to 10 1/s. Evaluation takes place via linearregression in the linear range.

The viscosity figures and paste properties of the crosslinkablecompositions of the invention are based on measurement in accordancewith DIN 54458 by means of the amplitude sweep. Measurement takes placevia a plate/plate arrangement with a cone 25 mm in diameter and with 0.5mm distance at a circular frequency of 10 Hz.

Viscosity η*(γ=0.1%): corresponds to the complex viscosity value [mPa*s]at a deformation of 0.1% according to DIN 54458. Viscosity η*(γ=100%):corresponds to the complex viscosity value [mPa*s] at a deformation of100% according to DIN 54458.

Yield point: corresponds to the shear stress [Pa] at the point at whichthe ratio of loss modulus to storage modulus is equal to 1.

The weight-average molar mass M_(w) and number-average molar mass M_(n)are determined in the context of the present invention by Size ExclusionChromatography (SEC) against polystyrene standard, in THF, at 60° C.,flow rate 1.2 ml/min and detection with RI (refractive index) detectoron a Styragel HR3-HR4-HR5-HR5 column set from Waters Corp. USA with aninjection volume of 100 μl.

The skin-forming time is defined as the time after which there is nolonger any adhering residue of a delivered string of silicone to apencil of hardness HB with which it is contacted.

The early strength is determined by applying a strip of silicone 10 mmwide and 6 mm in height to a plate of aluminum 0.25 mm thick, using adoctor blade, then bending one specimen in each case by 90° at 30-minuteintervals. The early strength reported is the time required for thesilicone strip to no longer exhibit any tear.

The Shore A hardness is determined according to DIN 53505-87(DIN=Deutsche Industrie Norm).

The elongation at break, tensile strength, and strain at 100% elongationare determined in accordance with DIN 53504-85 S2.

The 100% strain figure corresponds to the secant modulus at anelongation of 100%.

Hardness, elongation at break, 100% strain value, and tensile strengthafter climatic stress storage at 7d/70° C./95% relative atmospherichumidity are determined according to DIN 53505-87 and DIN 53504-85 S2,respectively, with the specimens initially vulcanizing for 14 days at23° C./50% relative atmospheric humidity and then being stored in aclimate cabinet for 7 days at 70° C. and 95% relative atmospherichumidity. After a rest time of 1 hour in the 23° C./50% relativeatmospheric humidity standard conditions, the specimens are measured asprescribed in the standards.

The accommodation of movement is tested in compliance with standard ASTMC719, by cleaning aluminum supports (76.2 mm×25.4 mm×6.4 mm, fromRocholl, 6016) with methyl ethyl ketone and pretreating them with primerG 791 (Wacker Chemie AG). After 24 hours, the specimens are produced,with the sealant being introduced in the required manner between twoaluminum supports, and the specimens are further conditioned accordingto ASTM C719 and subjected to measurement; classification takes placeaccording to ASTM C 920, chapter 4.

Inventive Example 1

100 parts of an α,ω-dihydroxydimethylpolysiloxane having a viscosity of80,000 mPa·s (OH content 470 wt. ppm) are mixed with 20 parts of atrimethylsilyl-endblocked polydimethylsiloxane having a viscosity of 100mPa·s, and the mixture is then homogenized with 90 parts of HEFanhydrite from Krone. Subsequently 11 parts of an acetoxysilane mixture(70 wt % ethyltrisacetoxysilane and 30 wt % methyltrisacetoxysilane) areadded and the mixture is homogenized. Subsequently 9 parts of apyrogenic silica having a BET surface area of 150 m²/g are mixed inhomogeneously and 0.04 part of di-n-butyltin diacetate is added. Themixture is devolatilized under a pressure of 100 mbar for 5 minutes.

Inventive Example 2

100 parts of an α,ω-dihydroxydimethylpolysiloxane having a viscosity of80,000 mPa·s (OH content 470 wt. ppm) are mixed with 20 parts of atrimethylsilyl-endblocked polydimethylsiloxane having a viscosity of 100mPa·s, and the mixture is then homogenized with 90 parts of HEFanhydrite from Krone. Subsequently 11 parts of an acetoxysilane mixture(70 wt % ethyltrisacetoxysilane and 30 wt % methyltrisacetoxysilane) areadded and the mixture is homogenized. Subsequently 9 parts of apyrogenic silica having a BET surface area of 150 m²/g are mixed inhomogeneously and 2 parts of Oktasoligen Strontium 10 from OMG areadded. The mixture is devolatilized under a pressure of 100 mbar for 5minutes.

Comparative Example 1

100 parts of an α,ω-dihydroxydimethylpolysiloxane having a viscosity of80,000 mPa·s (OH content 470 wt. ppm) are mixed with 20 parts of atrimethylsilyl-endblocked polydimethylsiloxane having a viscosity of 100mPa·s, and then 90 parts of talc 2/0 from Novotalk are mixed in.Subsequently 11 parts of an acetoxysilane mixture (70 wt %ethyltrisacetoxysilane and 30 wt % methyltrisacetoxysilane) are addedand the mixture is homogenized. Subsequently 9 parts of a pyrogenicsilica having a BET surface area of 150 m²/g are mixed in homogeneously,and 0.04 part of di-n-butyltin diacetate is added. The mixture isdevolatilized under a pressure of 100 mbar for 5 minutes.

Comparative Example 2

100 parts of an α,ω-dihydroxydimethylpolysiloxane having a viscosity of80,000 mPa·s (OH content 470 wt. ppm) are mixed with 20 parts of atrimethylsilyl-endblocked polydimethylsiloxane having a viscosity of 100mPa·s, and then homogenized with 90 parts of Polestar 200 from Imerys(kaolin). Subsequently 11 parts of an acetoxysilane mixture (70 wt %ethyltrisacetoxysilane and 30 wt % methyltrisacetoxysilane) are addedand the mixture is homogenized. Subsequently 9 parts of a pyrogenicsilica having a BET surface area of 150 m²/g are mixed in homogeneously,and 0.04 part of di-n-butyltin diacetate is mixed in. The mixture isdevolatilized under a pressure of 100 mbar for 5 minutes.

The product properties are summarized in the table.

TABLE Inventive example or comparative experiment 1 2 C1 C2 \Viscosity[mPa · s] 571,000 633,000 513,000 665,000 η* (γ = 0.1%) Viscosity [mPa ·s] 112,000 106,000 83,400 75,500 η* (γ = 100%) Yield point [Pa · s] 623778 622 529 Skin-forming time [min] 20 30 17 13 Shore A hardness 28 2329 35 Elongation at break [%] 670 800 530 320 Tensile strength [N/mm²]1.2 1.2 1.4 2.7 100% strain value [N/mm²] 0.43 0.36 0.57 1.18 LMclassification yes yes no no Accommodation of 25% x x x — movement asper ASTM 40% x x — — C719* 50% — x — — Paste storage 56 d at 50° C.Skin-forming time [min] 27 28 23 19 Shore A hardness 22 38 27 22Elongation at break [%] 710 830 480 400 Tensile strength [N/mm²] 1.2 1.11.2 1.5 100% strain value [N/mm²] 0.40 0.30 0.55 0.49 *complies (x);does not comply (—)

The inventive examples exhibit surprisingly high accommodation ofmovement of greater than or equal to 40% according to ASTM C719. Incontrast to the comparative examples with talc and kaolin, the inventiveexamples have a modulus of elasticity of less than 0.45 N/mm² and aretherefore classed as “low modulus” products (classification according toISO 11600).

In the accelerated aging test over 8 weeks (56d) at 50° C., theinventive compositions exhibit virtually no change in behavior. Bycomparison with this, the kaolin-filled compositions are not storagestable; hardness and modulus suffer severely on accelerated pastestorage at 50° C. Talc-filled compositions are storage-stable, butachieve only relatively low accommodation of movement and do not attainthe class of the “low modulus” products according to ISO 11600.

In spite of high filling levels, the products are readily applicablefrom the cartridge and have good processing behavior in terms ofextrusion rate and stringing.

1.-6. (canceled)
 7. An organopolysiloxane composition crosslinkable bycondensation reaction, and produced from a composition comprising: (1)at least one organopolysiloxane containing condensable end groups, (2)at least one organosilicon compound containing at least three acyloxygroups bonded directly to silicon, (3) one or more condensationcatalysts, (4) anhydrite, and (5) silica, in amounts of at least 1 andnot more than 15 parts by weight, based on 100 parts by weight oforganopolysiloxane (1), with the proviso that (6) no kaolin is used, (7)any further fillers are used in amounts of at most 25 parts by weightbased on 100 parts by weight of organopolysiloxanes (1), and (8)optionally further substances, useful in compositions crosslinkable bycondensation reaction and which are different from the constituents (1)to (7).
 8. The organopolysiloxane composition of claim 7, wherein silicais present in amounts of at least 1 and not more than 10 parts byweight, based on 100 parts by weight of organopolysiloxane (1).
 9. Theorganopolysiloxane composition of claim 7, wherein silica is present inamounts of at least 1 and not more than 15 parts by weight, based on 100parts by weight of organopolysiloxane (1), and any further fillers areused in amounts of at most 15 parts by weight based on 100 parts byweight of organopolysiloxanes (1).
 10. An organopolysiloxane compositionof claim 7, wherein silica is present in amounts of at least 1 and notmore than 15 parts by weight, based on 100 parts by weight, and anyfurther fillers are used in amounts of at most 5 parts by weight basedon 100 parts by weight of organopolysiloxanes (1).
 11. Theorganopolysiloxane composition of claim 7, wherein condensationcatalysts (3) comprise tin-free condensation catalysts.
 12. Theorganopolysiloxane composition of claim 7, wherein no further fillers(7) are present.
 13. The organopolysiloxane composition of claim 7,wherein further substances (8) are present, and comprise one or moresubstances selected from the group consisting of plasticizers,fungicides, adhesion promoters, rheological additives, pigments, andmixtures thereof.
 14. A method for producing the composition of claim 7,comprising mixing all of the constituents in any order.
 15. A moldingproduced by crosslinking a composition of claim 7.